The present invention relates to a pneumatically or electromotively operable disc brake for a commercial vehicle, having a brake caliper which straddles a brake disc, and having at least one brake application device for applying the disc brake. The brake application device has at least one pressure piece on its side which faces the brake disc, which pressure piece is sealed off, with respect to the brake caliper, or a part which is connected to the brake caliper, by a deformable bellows which is preferably connected to the brake caliper, or the part connected to the caliper, and to the pressure piece.
The principle construction of a disc brake of this type is known, for example, from DE 195 15 063 C2.
Here, the brake application device has two adjusting spindles, which are mounted displaceably in the brake caliper and bear, in each case, one pressure piece at their end which faces the brake disc. The pressure pieces press against a brake lining which makes contact with the brake disc in operation. The brake linings are held in the brake carrier and have force applied to them by the pressure pieces.
In order to protect the interior of the brake caliper and the adjusting spindles against soiling, a bellows in the form of a folding bellows is fastened to the respective pressure piece, which bellows is fixed at its other end to a closure plate, by which the brake caliper is closed. To this extent, the closure plate is an integral constituent part of the brake caliper. The bellows may also act directly on the brake caliper if no closure plate is provided.
Disc brakes of the above-mentioned type, that is to say those customarily mounted in commercial vehicles, are subjected to considerable loading in operation, in particular with regard to thermal loading. The frictional heat which is generated during braking is transmitted to a significant extent to the individual components of the disc brake, in particular also to the bellows of the respective pressure piece, which bellows acts as a sealing element.
The bellows which have been used up to now consist of a plastic, preferably of silicone. However, it would be desirable to use a material which is even more suitable for the bellows, in order to extend the maintenance intervals with regard to the bellows.
It is also desirable to use material which may be subjected to greater mechanical loading and is even less sensitive to soiling and damage, as can be produced, for example, by lining abrasion and rocks, stones, sand or the like, which fly around during driving.
Although attempts have already been made to reduce or preclude the mechanical loading via a cover, which cover is pushed over the bellows, for example in the form of a helical spring made from metal, this leads to additional thermal loading of the bellows as a result of a build-up of heat, with the result that this solution is entirely unsatisfactory.
The present invention is, therefore, based on the object of developing a disc brake of the above-mentioned type, such that its service life is increased and repair costs are reduced as a result.
This object is achieved by a disc brake for commercial vehicles wherein the bellows is composed of metal.
A disc brake which is configured in this way is distinguished, in particular, by the fact that its service life is increased substantially, that is to say the repair times, after which replacement of the bellows owing to wear is required, are substantially longer than has been the case up to now. This naturally results in cost advantages, as firstly the down time of the commercial vehicle is reduced and secondly assembly and material costs are lowered.
According to one advantageous development of the invention, the bellows are configured as folding bellows, for example in the form of lamellar or fluted bellows. Here, at least one, but preferably a plurality of flutes or folds are to be realized, in order to ensure a sufficient spring action.
Although metal folding bellows are known per se, for example from general textbooks such as Roloff/Matek: “Maschinenelemente” [Machine elements], 14th edition, pages 632, 633, and although a metal folding bellows 45 is known from DE 195 11 287 A1, the metal folding bellows shown there in no way serves for sealing, as there is a further folding bellows made from an elastomer with the designation for this purpose in the application. Rather, the folding bellows made from metal serve to produce a torsionally strong connection for transmitting torsional moments from the tensile stress force emanating from the threaded adjusting spindle between the force transmission plate with projection and the threaded spindle. Here, there is no connection to the brake caliper or to a part which is connected to the brake caliper, such as a cover which closes an opening in the brake caliper. Therefore, counter to the recommendations of the manufacturers, a metal folding bellows is used in this document as an element which transfers torque and not, for instance, as a connection between a pressure piece and a brake caliper or a part which is connected to the brake caliper, for sealing off the interior of the brake caliper.
Metal folding bellows are also known from U.S. Pat. No. 3,512,497. In this document, there is also no provision in any way, however, to use the metal folding bellows as a sealing element between a brake caliper and a pressure piece.
The use of a metal folding bellows in the manner according to the invention has not been considered previously, presumably since it was thought that the torque which the metal folding bellows exerts in each case on the control spindles on account of its spring action between the pressure piece and the brake caliper stands in the way of said use, in particular as the spring action and thus the torque change continuously as the lining wear increases and the folding bellows extends increasingly. According to the idea of the invention, however, it is surprisingly entirely possible to govern this effect. To be precise, in particular if the folding bellows is designed such that the thread holding moment, which is produced by the spring force of the metallic folding bellows and which the folding bellows exerts on the control spindles, is made small such that the adjusting function of the adjusting device on the adjusting spindles remains ensured by rotation of the control spindles and is not impaired (or not impaired significantly or to a practically considerable extent). Only if this condition is fulfilled does the function of adjustment remain ensured to a sufficient extent. The spring force is preferably smaller than 1000 N, in particular smaller than 800 N. These force details relate to two folding bellows. Per folding bellows, the following preferably holds: spring force <500 N, in particular <400 N.
It is also contemplated that the folding bellows is designed in such a way that, in the event of unworn brake linings and in the event of worn brake linings, it acts as a tension spring (or as a compression spring) on the adjusting spindles.
The folding bellows is preferably manufactured from a noncorroding metal. Here, lightweight metal or, in particular, stainless steel are possible. The folding bellows is manufactured, in particular, with the use of a laser welding process.
In addition to the high thermal and mechanical loadability, a bellows of this type is distinguished by the fact that it is deformable in a fluid-tight and permanently elastic manner.
The latter permits the multiple use of the bellows, that is to say it can also be used in the case of a plurality of brake lining changes, it being possible for the bellows to be deformed back into its initial state after the brake lining has been replaced.
As the shape and configuration of the novel bellows are expediently adapted to those of a known bellows, there is also the theoretical possibility of retrofitting. In the case of a necessary change, the novel bellows can therefore be used. The metal bellows as a constituent part of the original equipment may, of course, also be replaced per se by a novel metal bellows.
As a result of the adaptation of the novel bellows to the shape of the previously used bellows, it is also not necessary to change the other components of the disc brake to which the bellows can be connected. Rather, with appropriate adaptation, the bellows according to the invention may also theoretically be installed into an existing disc brake, in particular into the available installation space. It can, however, also be necessary to modify the installation conditions slightly, as the metal bellows is generally somewhat longer than a silicone bellows.
The production of the novel bellows is also very simple and inexpensive, as use may be made of known technologies, which permit economical production, above all under the aspect that bellows of this type are series-produced products, which are used in large numbers.
On account of the extension (tensile and compressive) rigidity of the bellows, the adjusting spindle, which is connected to the pressure piece, guided in the brake caliper and configured as a threaded spindle, is secured against unintended rotation as a result of vibrations and the like, with the result that, in some circumstances, a frictional securing element which has previously been required for this purpose may be omitted, at any rate in the event of a design as a pure compression spring. In some circumstances, the bellows may also be combined with a sealing ring section, at least at one of its ends.
The metal bellows may be fastened to the pressure piece by welding, soldering, roll forming, pinching, pressing with or without a press ring or by being held by means of a plate for thermal insulation which can be fixed to the pressure piece.
The connection to the brake caliper or the connected closure plate may be effected in the same way, it being possible for the closure plate to have a pot-shaped depression, to the base of which one end of the bellows is fastened, while the other end is fastened to the pressure piece.
In this case, the bellows extends coaxially with respect to the adjusting spindle which is arranged on the pressure piece.
According to a further advantageous embodiment, in the event of unworn brake linings, the bellows has an at least partially rolled up cover in its initial position, such that, as the lining wear increases, the rolled up region of the folding bellows can be extended gradually out of the rolled up region. In the event of a lining change, this “single use bellows” is then also replaced by a new one.
Further advantageous configurations of the invention are described and claimed herein.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.